Spatial arrangements of light emitters, photodetectors and signal processing electronics are vital components of many optical communications, data storage and measurement systems. In order to improve device performance and reduce manufacturing costs, there has been considerable effort aimed towards opto-electronic device integration. There is a well established art concerning the integration of photodetectors with electronic circuitry. For example, systems, such as cameras, based on the charge-coupled-device (CCD) are common. In the prior art, there are also examples of the integration of laser diodes with power monitoring photodiodes. The practical integration of light emitters with either or both sensitive photodetectors and electronics has not been realized. The preferred embodiment of light emitters involves heavily doped compound semiconductor, such as GaAs and InP, substrates, while that of photodetectors and electronics involves lightly doped silicon substrates. This presents a substantial obstacle when a closely spaced arrangement of high performance light emitters and sensitive photodetectors is needed.
The following patent is representative of the need in the prior art for the practical implementation of devices based on the spatial arrangement of light emitters and photodetectors: "Active Electro-Optical Distance Detection Methods and Devices", by Daniel C. Abbas (U.S. Pat. No. 4,511,248, April 1985), describes an optical distance measuring device. Light from an emitter, located in the focal plane, is directed through a lens unto the target object. A portion of the light is reflected off the object and back through the lens forming a blur circle. The measurement technique is based on determining the size of the blur circle, by measuring the slope of its amplitude, using a pair of photodetectors and, hence, the distance to the object. This device has been constructed using a light-emitting-diode (LED) and a pair of photodiodes monolithically integrated on a substrate. It is not practical, at this point in time, to integrate the emitter, detector and electronic functions monolithically. As the dimensions, e.g., the separation of the LED from the detectors, are reduced to satisfy application requirements, the optical isolation of the light emitter from the photodetectors becomes an increasingly severe problem with the light from the emitter swamping the weak reflected signals.